12,844 research outputs found
A possible disk mechanism for the 23d QPO in Mkn~501
Optically thin two-temperature accretion flows may be thermally and viscously
stable, but acoustically unstable. Here we propose that the O-mode instability
of a cooling-dominated optically thin two-temperature inner disk may explain
the 23-day quasi-periodic oscillation (QPO) period observed in the TeV and
X-ray light curves of Mkn~501 during its 1997 high state. In our model the
relativistic jet electrons Compton upscatter the disk soft X-ray photons to TeV
energies, so that the instability-driven X-ray periodicity will lead to a
corresponding quasi-periodicity in the TeV light curve and produce correlated
variability. We analyse the dependence of the instability-driven
quasi-periodicity on the mass (M) of the central black hole, the accretion rate
() and the viscous parameter () of the inner disk. We
show that in the case of Mkn~501 the first two parameters are constrained by
various observational results, so that for the instability occurring within a
two-temperature disk where , the quasi-period is expected to
lie within the range of 8 to 100 days, as indeed the case. In particular, for
the observed 23-day QPO period our model implies a viscosity coefficient
, a sub-Eddington accretion rate and a transition radius to the outer standard disk of , and predicts a period variation due to the
motion of the instability region.Comment: 18 pages, 1 figure, accepted by AP
Naked Singularities in Spherically Symmetric Inhomogeneous Tolman-Bondi Dust Cloud Collapse
We investigate the occurrence and nature of naked singularity for the
inhomogeneous gravitational collapse of Tolman-Bondi dust clouds.It is shown
that the naked singularities form at the center of the collapsing cloud in a
wide class of collapse models which includes the earlier cases considered by
Eardley and Smarr and Christodoulou. This class also contains self-similar as
well as non-self-similar models. The structure and strength of this singularity
is examined and the question is investigated as to when a non-zero measure set
of non-spacelike trajectories could be emitted from the singularity as opposed
to isolated trajectories coming out. It is seen that the weak energy condition
and positivity of energy density ensures that the families of non-spacelike
trajectories come out of the singularity. The curvature strength of the naked
singularity is examined which provides an important test for its physical
significance and powerful curvature growth near the naked singularity is
pointed out for several subclasses considered. The conditions are discussed for
the naked singularity to be globally naked. Implications for the basic issue of
the final fate of gravitational collapse are considered once the
inhomogeneities in the matter distribution are taken into account. It is argued
that a physical formulation for the cosmic censorship may be evolved which
avoids the features above. Possibilities in this direction are discussed while
indicating that the analysis presented here should be useful for any possible
rigorous formulation of the cosmic censorship hypothesis.Comment: 41 pages, TIFR preprint TAP 9/9
On a q-difference Painlev\'e III equation: II. Rational solutions
Rational solutions for a -difference analogue of the Painlev\'e III
equation are considered. A Determinant formula of Jacobi-Trudi type for the
solutions is constructed.Comment: Archive version is already official. Published by JNMP at
http://www.sm.luth.se/math/JNMP
Modeling Aerial Gamma-Ray Backgrounds using Non-negative Matrix Factorization
Airborne gamma-ray surveys are useful for many applications, ranging from
geology and mining to public health and nuclear security. In all these
contexts, the ability to decompose a measured spectrum into a linear
combination of background source terms can provide useful insights into the
data and lead to improvements over techniques that use spectral energy windows.
Multiple methods for the linear decomposition of spectra exist but are subject
to various drawbacks, such as allowing negative photon fluxes or requiring
detailed Monte Carlo modeling. We propose using Non-negative Matrix
Factorization (NMF) as a data-driven approach to spectral decomposition. Using
aerial surveys that include flights over water, we demonstrate that the
mathematical approach of NMF finds physically relevant structure in aerial
gamma-ray background, namely that measured spectra can be expressed as the sum
of nearby terrestrial emission, distant terrestrial emission, and radon and
cosmic emission. These NMF background components are compared to the background
components obtained using Noise-Adjusted Singular Value Decomposition (NASVD),
which contain negative photon fluxes and thus do not represent emission spectra
in as straightforward a way. Finally, we comment on potential areas of research
that are enabled by NMF decompositions, such as new approaches to spectral
anomaly detection and data fusion.Comment: 14 pages, 12 figures, accepted for publication in IEEE Transactions
on Nuclear Scienc
Phase diagram and symmetry breaking of SU(4) spin-orbital chain in a generalized external field
The ground state phases of a one-dimensional SU(4) spin-orbital Hamiltonian
in a generalized external field are studied on the basis of Bethe-ansatz
solution. Introducing three Land\'e factors for spin, orbital and their
products in the SU(4) Zeeman term, we discuss systematically the various
symmetry breaking. The magnetization versus external field are obtained by
solving Bethe-ansatz equations numerically. The phase diagrams corresponding to
distinct residual symmetries are given by means of both numerical and
analytical methods.Comment: Revtex4, 16 pages, 7 figure
Quantum state engineering in hybrid open quantum systems
We investigate a possibility to generate nonclassical states in light-matter coupled noisy quantum systems, namely, the anisotropic Rabi and Dicke models. In these hybrid quantum systems, a competing influence of coherent internal dynamics and environment-induced dissipation drives the system into nonequilibrium steady states (NESSs). Explicitly, for the anisotropic Rabi model, the steady state is given by an incoherent mixture of two states of opposite parities, but as each parity state displays light-matter entanglement, we also find that the full state is entangled. Furthermore, as a natural extension of the anisotropic Rabi model to an infinite spin subsystem, we next explored the NESS of the anisotropic Dicke model. The NESS of this linearized Dicke model is also an inseparable state of light and matter. With an aim to enrich the dynamics beyond the sustainable entanglement found for the NESS of these hybrid quantum systems, we also propose to combine an all-optical feedback strategy for quantum state protection and for establishing quantum control in these systems. Our present work further elucidates the relevance of such hybrid open quantum systems for potential applications in quantum architectures
Time-dependent CP Asymmetries in Decays
We report the first measurement of CP-violation parameters in B^0 ->
K_S^0\rho^0\gamma decays based on 657 million B\bar B pairs collected with the
Belle detector at the KEKB asymmetric-energy collider. We measure the
time-dependent CP violating parameter S_{K_S^0\rho^0\gamma}= 0.11 +/-
0.33(stat.)^{+0.05}_{-0.09}(syst.). We also obtain the effective direct CP
violating parameter A_eff=0.05 +/- 0.18(stat.) +/- 0.06(syst.) for
m_{K_S\pi^+\pi^-}<1.8 GeV/c^2 and 0.6 GeV/c^2<m_{\pi^+\pi^-}<0.9 GeV/c^2.Comment: 6 pages, 3 figures, to be submitted to PR
Mobile Object Tracking in Panoramic Video and LiDAR for Radiological Source-Object Attribution and Improved Source Detection
The addition of contextual sensors to mobile radiation sensors provides
valuable information about radiological source encounters that can assist in
adjudication of alarms. This study explores how computer-vision based object
detection and tracking analyses can be used to augment radiological data from a
mobile detector system. We study how contextual information (streaming video
and LiDAR) can be used to associate dynamic pedestrians or vehicles with
radiological alarms to enhance both situational awareness and detection
sensitivity. Possible source encounters were staged in a mock urban environment
where participants included pedestrians and vehicles moving in the vicinity of
an intersection. Data was collected with a vehicle equipped with 6 NaI(Tl) 2
inch times 4 inch times 16 inch detectors in a hexagonal arrangement and
multiple cameras, LiDARs, and an IMU. Physics-based models that describe the
expected count rates from tracked objects are used to correlate vehicle and/or
pedestrian trajectories to measured count-rate data through the use of Poisson
maximum likelihood estimation and to discern between source-carrying and
non-source-carrying objects. In this work, we demonstrate the capabilities of
our source-object attribution approach as applied to a mobile detection system
in the presence of moving sources to improve both detection sensitivity and
situational awareness in a mock urban environment
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